They have announced it here: http://www.phpbb.com/community/viewtopic.php?f=14&t=2099641
and it is a result of their experiences here: http://blog.phpbb.com/2010/07/28/oscon-2010/
I think whilst normally we want to improve the core forum module, this feels like it could be different. If the phpbb team are working on an official bridge they have the ability to change the code of phpbb itself to make it integrate generally. (Which they appear to be doing anyway).
They are working on rebuilding phpbb4 from the ground-up using the symphony2 framework and drupal is always almost rebuilt. If this bridge is good maybe Drupal8 and phpbb4 could be so tightly integrated there would be no need for a forum module?
Do you think this future is desirable? Or impossible? What do you think gets in the way of this?